The vestibulocochlear nerve (CN VIII) has both a vestibular and cochlear component. The vestibular component senses balance and equilibrium via the vestibular ganglia, while the cochlear component is responsible for hearing via the spiral ganglia. Damage to CN VIII can result in symptoms like vertigo, hearing loss, and tinnitus. Lesions of the vestibular branch cause vestibular neuritis with vertigo and nystagmus, while lesions of both vestibular and cochlear branches cause labyrinthitis with additional symptoms of hearing loss and tinnitus.

3. Outline for Each Cranial Nerve
• Origin & point of attachment in brainstem
• Course – Any significance!!!
• Point of exit from or entry into skull (Foramen)
• Distribution/Function (Motor,
parasympathetic,
sensory, special sensation)
• Dysfunction in case of lesion

4. Classification
 Sensory: only afferent (sensory) fibers
 N. Olfactorius
 N. Opticus
 N. Vestibulocochlearis
 Motor: only efferent (motor) fibers
 N. Oculomotorius
 N. Trochlearis
 N. Abducens
 N. Accessorius
 N. Hypoglossus
 Mixed: sensory and motor fibers
 N. Trigeminalis
 N. Facialis
 N. Glossopharyngeus
 N. Vagus

5. Olfactory Nerve (I)
• Origin: 20 neurons from mucosa
of upper part of nasal cavity:
Pass via cribriform foramina
• End: Olfactory bulb (largest
neuron called mitral cell)
• Olfactory tracts from bulb divide
into lateral & medial striae
• Lateral stria →lateral olfactory
area of cerebral cortex
• Medial stria → opposite olfactory
bulb via anterior commissure

7. CN I Olfactory: Function & applied
• Function: smell
• Dysfunction: Anosmia – loss
of olfaction
• Applied
▫ Head injury may tear nerves
filaments passing through
cribriform plate especially in
fractures involving anterior cranial
fossa
▫ Leakage of CSF through nose (CSF
rhinorrhoea) from tearing of
meningeal covering of nerve

8. Oculomotor Nerve (III)
Origin: Oculomotor Nucleus (Motor) & Edinger-Westphal
(Parasympathetic)
• Course: Lies on medial side of crus cerebri, along lateral
wall of cavernous sinus;
enter orbit through superior orbital fissure. Divides into
superior & inferior
divisions
• Parasympathetic fibres pass via inferior division

10. Distribution: Extraocular muscles
▫ Superior, inferior, medial recti, inferior oblique,
levator palpebral
superioris
▫ Sphincter pupillae muscle of iris & ciliary muscle
constricts pupil& accommodates lens

11. Dysfunction
• Eye deviation - down & out (Lateral stabismus)
▫ lateral rectus & superior oblique unopposed.
• Ptosis (drooping of eyelid)
• Mydriasis (fully dilated pupil)
• Loss of power of accommodation
• Diplopia

12. Trochlear Nerve (IV)
• Origin: Trochlear Nucleus. Most slender of cranial nerves
• Course:smallest cranial nerve Only nerve to emerge from
dorsal part of brainstem
& its fibres cross. Passes onto lateral wall of
cavernous sinus, then superior orbital fissure
• Distribution: Superior oblique
• Dysfunction: Rarely paralysed alone
▫ Diplopia (double vision) on looking down & Extorsion

14. Trigeminal Nerve
Largest CN
Origin:Motor Nucleus
Sensory Nucleus:
mesencephalic Nuc.
pontine (chief) &
spinal Nuc
Has 3 divisions:
Ophthalmic
Maxillary
Mandibular
The trigeminal nerve is
associated with derivatives
of the 1st pharyngeal arch.

15. 1-Ophthalmic Division (V1 )
-superior orbital fissure
2-Maxillary Division (V2 )
-foramen rotundum
3-Mandibular Division (V3 )
-foramen ovale

16. Ophthalmic Nerve [V1]
Ophthalmic nerve gives rise to 3 terminal branches: frontal, lacrimal and nasociliary,
which innervate the skin and mucous membrane of derivatives of the frontonasal
prominence derivatives:
Forehead and scalp
Frontal and ethmoidal sinus
Upper eyelid and its conjunctiva
Cornea (see clinical relevance)
Dorsum of the nose
Parasympathetic Supply:
Lacrimal gland: Post ganglionic fibres from the pterygopalatine ganglion (derived
from the facial nerve), travel with the zygomatic branch of V2 and then join the
lacrimal branch of V1. The fibres supply parasympathetic innervation to to the lacrimal
gland.

18. Maxillary nerve [V2]
Maxillary nerve gives rise to 14 terminal branches, which innervate the skin, mucous
membranes and sinuses of derivatives of the maxillary prominence of the 1st pharyngeal arch:
Lower eyelid and its conjunctiva
Cheeks and maxillary sinus
Nasal cavity and lateral nose
Upper lip
Upper molar, incisor and canine teeth and the associated gingiva
Superior palate
Parasympathetic Supply:
Lacrimal gland: Post ganglionic fibres from the pterygopalatine ganglion (derived from the
facial nerve), travel with the zygomatic branch of V2 and then join the lacrimal branch of V1.
The fibres supply parasympathetic innervation to the lacrimal gland.
Nasal glands: Parasympathetic fibres are also carried to the mucous glands of the nasal
mucosa. Post-ganglionic fibres travel with the nasopalatine and greater palatine nerves
(branches of V2)

21. Mandibular Nerve
The mandibular nerve is the largest of the three divisions of the
trigeminal nerve. It arises, within the cranium, from the lower part of the
convex border of the trigeminal ganglion, and enters the infratemporal
fossa through the foramen ovale. Until it leaves the skull it is composed
(like the ophthalmic and maxillary branches of the trigeminal) wholly of
sensory fibers. But, as it descends through the foramen ovals, it is joined
by the motor root of the trigeminal nerve; and, below the skull, it is
therefore a mixed nerve.
Immediately after its exit from the skull, the mandibular nerve gives off
the nervus spinosus and the nerve to the medial pterygoid muscle, and, at
a slightly lower level, it divides into an anterior division and a posterior
division.

23. The anterior division is composed chiefly of motor fibers.
It divides almost at once into the deep temporal nerves, the
nerves to the masseter and lateral pterygoid, and the buccal
nerve; all its sensory fibers pass into the buccal nerve.
The posterior division gives off the two roots of the
auriculotemporal nerve and then divides into the lingual and
the inferior alveolar. The only motor fibers in it are those that
form the mylohyoid branch of the inferior dental.
The nervus spinosus is a very slender branch which enters
the cranium with the middle meningeal artery through the
foramen spinosum. It supplies the dura mater, and sends a
filament into a middle ear.

24. The lingual nerve is almost as thick as the inferior
dental. It is entirely sensory and is distributed to the
mucous membrane of the anterior two-thirds of the
tongue (general sensation)
it is joined by the chorda tympani branch of the facial
nerve that carries taste from the anterior tow thirds of
the tongue

25. These branches of the mandibular nerve innervate the skin, mucous
membrane and striated muscle derivatives of the mandibular prominence of the
1st pharyngeal arch.
Sensory supply:
Mucous membranes and floor of the oral cavity
External ear
Lower lip
Chin
Anterior 2/3 of the tongue (only general sensation; special taste sensation
supplied by the chorda tympani, a branch of the facial nerve)
Lower molar, incisor and canine teeth and the associated gingiva
Motor Supply:
Muscles of mastication; medial pterygoid, lateral pterygoid, masseter,
temporalis
Anterior belly of the digastric muscle (part of the suprahyoid muscles)
Tensor veli palatini
Tensor tympani

26. Parasympathetic Supply:
Submandibular and Sublingual glands: Post-ganglionic
fibres from the submandibular ganglion (derived from the
facial nerve through chorda tympani), travel with the lingual
nerve to innervate these glands.
Parotid gland: Post-ganglionic fibres from the otic
ganglion (derived from the glossopharyngeal nerve, CN IX
through tympanic branch of IX then smaller petrosal n then
to otic ganglion to th AT n), travel with the auricotemporal
branch of the V3 to innervate the parotid gland.

27. • Trigeminal Nerve dysfunction
• Trigeminal neuralgia – pain in distribution of maxillary
and/or mandibular nerve.
• Decreased forehead pain and touch, corneal reflex (1st
sign of lesion of ophthalmic
nerve), cheek touch & pain, jaw touch & pain & jerk, and
weakness of muscles of mastication

28. Abducens Nerve CN(VI)
• Origin: Abducens nucleus
• Course: It has the longest subarachnoid course of all
the cranial nerves.
• Emerges between pons & medulla, passes through
cavernous sinus
• Enters orbit through superior orbital fissure
• Distribution: Supplies Lateral rectus
• Dysfunction: Medial deviation & diplopia. Cannot look
outwards

30. Vestibulocochlear Nerve (VIII)
 Functions: Special sensory (special somatic afferent)
that is, special sensations of hearing and equilibrium.
 Nuclei: Four vestibular nuclei are located at the
junction of the pons and medulla in the lateral part of
the floor of the 4th ventricle; two cochlear nuclei are
in the medulla.
 The vestibulocochlear nerve (CN VIII) emerges from
the junction of the pons and medulla and enters the
internal acoustic meatus. Here it separates into the
vestibular and cochlear nerves.

31.  The vestibular nerve is concerned with equilibrium. It
is composed of the central processes of bipolar
neurons in the vestibular ganglion; the peripheral
processes of the neurons extend to the maculae of the
utricle and saccule (sensitive to the line of linear
acceleration relative to the position of the head) and to
the ampullae of the semicircular ducts (sensitive to
rotational acceleration).
 The cochlear nerve is concerned with hearing. It is
composed of the central processes of bipolar neurons
in the spiral ganglion; the peripheral processes of the
neurons extend to the spiral organ.

32. The Vestibulocochlear Nerve (CN VIII)
 It is comprised of two parts – vestibular fibres and cochlear fibres. Both
have a purely sensory function.
 The vestibular and cochlear portions of the vestibulocochlear nerve are
functionally discrete, and so originate from different nuclei in the brain:
 Vestibular component – arises from the vestibular nuclei complex in the
pons and medulla.
 Cochlear component – arises from the ventral and dorsal cochlear
nuclei, situated in the inferior cerebellar peduncle.
 Both sets of fibres combine in the pons to form the vestibulocochlear
nerve. The nerve emerges from the brain at the cerebellopontine angle
and exits the cranium via the internal acoustic meatus of the temporal
bone.
 Within the distal aspect of the internal acoustic meatus, the
vestibulocochlear nerve splits, forming the vestibular nerve and the
cochlear nerve. The vestibular nerve innervates the vestibular system of
the inner ear, which is responsible for detecting balance. The cochlear
nerve travels to cochlea of the inner ear, forming the spiral ganglia which
serve the sense of hearing.

34.  Special Sensory Functions
 The vestibulocochlear nerve is unusual in that it primarily
consists of bipolar neurones. It is responsible for the special
senses of hearing (via the cochlear nerve), and balance (via the
vestibular nerve).
 Clinical Relevance: Basilar Skull Fracture
 A basilar skull fracture is a fracture of the skull base, usually
resulting from major trauma. The vestibulocochlear nerve can be
damaged within the internal acoustic meatus, producing
symptoms of vestibular and cochlear nerve damage.
 Patients may also exhibit signs related to the other cranial
nerves, bleeding from the ears and nose, and cerebrospinal fluid
leaking from the ears (CSF otorrhoea) and nose (CSF
rhinorrhoea).

35.  Hearing
 The cochlea detects the magnitude and frequency of sound waves. The inner hair
cells of the organ of Corti activate ion channels in response to vibrations of the
basilar membrane. Action potentials travel from the spiral ganglia, which house
the cell bodies of neurones of the cochlear nerve.
 The magnitude of the sound determines how much the membrane vibrates and
thereby how often action potentials are triggered. Louder sounds cause the
basilar membrane to vibrate more, resulting in action potentials being
transmitted from the spiral ganglia more often, and vice versa. The frequency of
the sound is coded by the position of the activated inner hair cells along the
basilar membrane.
 Equilibrium (Balance)
 The vestibular apparatus senses changes in the position of the head in relation to
gravity. The vestibular hair cells are located in the otolith organs (the utricule and
saccule), where they detect linear movements of the head, as well as in the three
semicircular canals, where they detect rotational movements of the head. The cell
bodies of the vestibular nerve are located in the vestibular ganglion which is
housed in the outer part of the internal acoustic meatus.
 Information about the position of the head is used to coordinate balance and the
vestibulo-ocular reflex. The vestibulo-ocular reflex (also called the
oculocephalic reflex) allows images on the retina to be stabilised when the head is
turning by moving the eyes in the opposite direction. It can be demonstrated by
holding one finger still at a comfortable distance in front of you and twisting your
head from side to side whilst staying focused on the finger.

36.  Clinical Relevance: Vestibular Neuritis
 Vestibular neuritis refers to inflammation of the vestibular branch of the
vestibulocochlear nerve. The aetiology of this condition is not fully
understood, but some cases are thought to be due to reactivation of the herpes
simplex virus.
 It presents with with symptoms of vestibular nerve damage:
 Vertigo – a false sensation that oneself or the surroundings are spinning or
moving.
 Nystagmus – a repetitive, involuntary to-and-fro oscillation of the eyes.
 Loss of equilibrium (especially in low light).
 Nausea and vomiting.
 The condition is usually self-resolving. Treatment is symptomatic, usually in
the form of anti-emetics or vestibular suppressants
 Clinical Relevanace: Labyrinthitis
 Labyrinthitis refers to inflammation of the membranous labyrinth, resulting in
damage to the vestibular and cochlear branches of the vestibulocochlear nerve.
 The symptoms are similar to vestibular neuritis, but also include indicators of
cochlear nerve damage:
 Sensorineural hearing loss.
 Tinnitus – a false ringing or buzzing sound.

37.  Acoustic Neuroma Symptoms (vestibular
schwannoma)
 The early symptoms of an acoustic neuroma are often
subtle. Many people attribute the symptoms to normal
changes of aging, so it may be a while before the
condition is diagnosed.
 The first symptom is usually a gradual loss of hearing in
one ear, often accompanied by (tinnitus) or a feeling of
fullness in the ear. Less commonly, acoustic neuromas
may cause sudden hearing loss.
 Other symptoms, which may occur over time, include:
 Problems with balance
 Vertigo (feeling like the world is spinning)
 Facial numbness and tingling, which may be
constant or come and go
 Facial weakness
 Taste changes
 Difficulty swallowing and hoarseness
 Headaches
 Clumsiness or unsteadiness
 Confusion

38. Glossopharyngeal Nerve (CN IX)
 originates in the medulla oblongata of the brain. It
emerges from the anterior aspect of the medulla.
 Nuclei: Four nuclei in the medulla send or receive fibers via
CN IX: two motor and two sensory. Three of these nuclei
are shared with CN X.
 moving laterally in the posterior cranial fossa. The nerve
leaves the cranium via the jugular foramen. At this point,
the tympanic nerve arises.
 It has a mixed sensory and parasympathetic composition.
 Immediately outside the jugular foramen lie two ganglia
(collections of nerve cell bodies). They are known as the
superior and inferior (or petrous) ganglia – they
contain the cell bodies of the sensory fibres in the
glossopharyngeal nerve.

40.  Innervates:
 motor: Innervates the
stylopharyngeus muscle
of the pharynx. wich acts to
shorten and widen the
pharynx, and elevate the
larynx during swallowing.
 Sensory to to the carotid
sinus and body
 Parasympathetic: Provides
parasympathetic
innervation to the parotid
gland.
 Special Sensory: Provides
taste sensation to the
posterior 1/3 of the tongue.
 Sensory: Innervates the
oropharynx, carotid body
and sinus, posterior 1/3 of
the tongue, middle ear
cavity and Eustachian
tube.

41.  The glossopharyngeal nerve terminates by splitting
into several sensory branches:
 Pharyngeal branch – combines with fibres of the vagus
nerve to form the pharyngeal plexus. It innervates the mucosa
of the oropharynx.
 Lingual branch – provides the posterior 1/3 of the tongue
with general and taste sensation
 Tonsillar branch – forms a network of nerves, known as
the tonsillar plexus, which innervates the palatine tonsils.
 he glossopharyngeal nerve provides parasympathetic
innervation to the parotid gland.
 These fibres originate in the inferior salivatory nucleus of CN
IX. These fibres travel with the tympanic nerve to the middle
ear. From the ear, the fibres continue as the lesser petrosal
nerve, before synapsing at the otic ganglion.
 The fibres then hitchhike on the auriculotemporal nerve to
the parotid gland, where they have a secretomotor effect.

42. Clinical Relevance
 Gag Reflex
 The glossopharyngeal nerve supplies sensory innervation
to the oropharynx, and thus carries the afferent
information for the gag reflex. When a foreign object
touches the back of the mouth, this stimulates CNIX,
beginning the reflex. The efferent nerve in this process is
the vagus nerve, CNX.
 An absent gag reflex signifies damage to the
glossopharyngeal nerve.

43. The Vagus Nerve (CN X)
 The vagus nerve is associated with the derivatives of the
fourth pharyngeal arch.
 The vagus nerve has the longest course of all the cranial
nerves, extending from the head to the abdomen.
 In the Head: The vagus nerve originates from the medulla
of the brainstem. It exits the cranium via the jugular
foramen, with the glossopharyngeal and accessory nerves.
 Within the cranium, the auricular branch arises.
This supplies sensation to the posterior part of the external
auditory and canal external ear.

44.  Several branches arise in the
neck:
 Pharyngeal branches –
Provides motor innervation to the
majority of the muscles of the
pharynx and soft palate.
 Superior laryngeal nerve –
Splits into internal and external
branches. The external laryngeal
nerve innervates the cricothyroid
muscle of the larynx. The internal
laryngeal provides sensory
innervation to the
laryngopharynx and superior part
of the larynx.
 Recurrent laryngeal
nerve (right side only) – Hooks
underneath the right subclavian
artery, then ascends towards to
the larynx. It innervates the
majority of the intrinsic muscles
of the larynx.

45.  In the thorax, the right vagus nerve
forms the posterior vagal trunk, and the
left forms the anterior vagal trunk.
Branches from the vagal trunks
contribute to the formation of the
oesophageal plexus, which innervates
the smooth muscle of the oesophagus.
 Two other branches arise in the thorax:
 Left recurrent laryngeal nerve – it
hooks under the arch of the aorta,
ascending to innervate the majority of
the intrinsic muscles of the larynx.
 Cardiac branches – these innervate
regulate heart rate and provide visceral
sensation to the organ.
 The vagal trunks enter the abdomen via
the oesophageal hiatus, an opening in
the diaphragm.
 In the abdomen, the vagal trunks
terminate by dividing into branches that
supply the oesophagus, stomach and the
small and large bowel (up to the splenic
flexure).

46.  Sensory Functions
 There are somatic and visceral components to the sensory
function of the vagus nerve.
 Somatic refers to sensation from the skin and muscles.
This is provided by the auricular nerve, which innervates
the skin of the posterior part of the external auditory canal
and external ear.
 Visceral sensation is that from the organs of the body.
The vagus nerve innervates:
 Laryngopharynx – via the internal laryngeal nerve.
 Superior aspect of larynx (above vocal folds) – via the
internal laryngeal nerve.
 Heart – via cardiac branches of the vagus nerve.
 Gastro-intestinal tract (up to the splenic flexure) – via
the terminal branches of the vagus nerve.

47.  Motor Functions
 The vagus nerve innervates
the majority of the muscles
associated with the pharynx
and larynx. These muscles are
responsible for the initiation
of swallowing and phonation.
 Muscles of the Pharynx: Most
of the muscles of the pharynx
are innervated by the
pharyngeal branches of the
vagus nerve:
 Superior, middle and
inferior pharyngeal
constrictor muscles
 Palatopharyngeus
 Salpingopharyngeus
 Muscles of the Larynx

48.  Parasympathetic Functions:
 In the thorax and abdomen, the vagus nerve is the main
parasympathetic outflow to the heart and gastro-intestinal organs.
 The Heart
 Cardiac branches arise in the thorax, conveying parasympathetic
innervation to the sino-atrial and atrio-ventricular nodes of the heart
(For more heart anatomy, see here).
 These branches stimulate a reduction in the resting heart rate. They are
constantly active, producing a rhythm of 60 – 80 beats per minute. If
the vagus nerve was lesioned, the resting heart rate would be around
100 beats per minute.
 Gastro-Intestinal System
 The vagus nerve provides parasympathetic innervation to the majority
of the abdominal organs. It sends branches to the oesophagus, stomach
and most of the intestinal tract – up to the splenic flexure of the large
colon.
 The function of the vagus nerve is to stimulate smooth muscle
contraction and glandular secretions in these organs. For example, in
the stomach, the vagus nerve increases the rate of gastric emptying,
and stimulates acid production.

58. The Accessory Nerve (CN XI)
 The accessory nerve is the eleventh paired cranial nerve. It has a purely
somatic motor function, innervating the sternocleidomastoid and
trapezius muscles.
 Anatomical Course
 Traditionally, the accessory nerve is divided into spinal and cranial
parts.
 The spinal portion arises from neurones of the upper spinal cord,
specifically C1-C5/C6 spinal nerve roots. These fibres coalesce to form
the spinal part of the accessory nerve, which then runs superiorly to
enter the cranial cavity via the foramen magnum.
 The nerve traverses the posterior cranial fossa to reach the jugular
foramen. It briefly meets the cranial portion of the accessory nerve,
before exiting the skull (along with the glossopharyngeal and vagus
nerves).

59.  Outside the cranium, the
spinal part descends along
the internal carotid artery to
reach the
sternocleidomastoid
muscle, which it innervates.
It then moves across the
posterior triangle of the
neck to supply motor fibres
to the trapezius.
 Note: The extracranial
course of the accessory
nerve is relatively superficial
(it runs between the
investing and prevertebral
layers of fascia), and thus
leaves it vulnerable to
damage.

60.  Cranial Part
 The cranial portion is much smaller, and arises from
the lateral aspect of the medulla oblongata. It leaves
the cranium via the jugular foramen, where it briefly
contacts the spinal part of the accessory nerve.
 Immediately after leaving the skull, cranial part
combines with the vagus nerve (CN X) at the inferior
ganglion of vagus nerve (a ganglion is a collection of
nerve cell bodies). The fibres from the cranial part are
then distributed through the vagus nerve. For this
reason, the cranial part of the accessory nerve is
considered as part of the vagus nerve.

61. Clinical Relevance
 Examination of the Accessory Nerve
 The accessory nerve is examined by asking the patient to rotate
their head and shrug their shoulders, both normally and against
resistance. Simply observing the patient may also reveal signs of
muscle wasting in the sternocleidomastoid and trapezius in cases of
long-standing nerve damage.
 Palsy of the Accessory Nerve
 The most common cause of accessory nerve damage is iatrogenic
(i.e. due to a medical procedure). In particular, operations such as
cervical lymph node biopsy or cannulation of the internal jugular
vein can cause trauma to the nerve.
 Clinical features include muscle wasting and partial paralysis of the
sternocleidomastoid, resulting in the inability to rotate the head or
weakness in shrugging the shoulders. Damage to the muscles may
also result in an asymmetrical neckline.

64. The Hypoglossal Nerve (CN XII)
 The nerve has a purely
somatic motor function,
innervating the majority of
the muscles of the tongue.
 The hypoglossal nerve
arises from the
hypoglossal nucleus in
the medulla oblongata of
the brain. It then passes
laterally across the
posterior cranial fossa,
within the subarachnoid
space. The nerve exits the
cranium via the
hypoglossal canal.

65.  Now extracranial, the
nerve receives a branch of
the cervical plexus that
conducts fibres from C1/C2
spinal nerve roots. These
fibres do not combine with
the hypoglossal nerve –
they merely travel within
its sheath.
 It then passes inferiorly to
the angle of the mandible,
crossing the internal and
external carotid arteries,
and moving in an anterior
direction to enter the
tongue.

66.  Motor Function
 The hypoglossal nerve is responsible
for motor innervation of the vast
majority of the muscles of the tongue
(except for palatoglossus). These
muscles can be subdivided into two
groups:
 i) Extrinsic muscles
 Genioglossus (makes up the bulk
of the tongue)
 Hyoglossus
 Styloglossus
 Palatoglossus (innervated by
vagus nerve)
 ii) Intrinsic muscles
 Superior longitudinal
 Inferior longitudinal
 Transverse
 Vertical

67.  Role of the C1/C2 Roots
 The C1/C2 roots that travel
with the hypoglossal nerve also
have a motor function. They
branch off to innervate the
geniohyoid (elevates the hyoid
bone) and thryohyoid
(depresses the hyoid bone)
muscles.
 Another branch containing
C1/C2 fibres descends to supply
the ansa cervicalis – a loop of
nerves that is part of the
cervical plexus. From the ansa
cervicalis, nerves arise to
innervate the omohyoid,
sternohyoid and sternthyroid
muscles. These muscles all act
to depress the hyoid bone.

68. Clinical Relevance
 Examination of the Hypoglossal Nerve
 The hypoglossal nerve is examined by asking the patient to protrude
their tongue. Other movements such as asking the patient to push their
tongue against their cheek and feeling for the pressure on the opposite
side of the cheek may also be used if damage is suspected.
 Palsy of the Hypoglossal Nerve
 Damage to the hypoglossal nerve is a relatively uncommon cranial
nerve palsy. Possible causes include tumours and penetrating
traumatic injuries. If the symptoms are accompanied by acute pain, a
possible cause may be dissection of the internal carotid artery.
 Patients will present with deviation of the tongue towards the damaged
side on protrusion, as well as possible muscle wasting and
fasciculations (twitching of isolated groups of muscle fibres) on the
affected side.